The US Food and Drug Administration is investigating 13 deaths that may be linked to consumption of an energy drink called 5-hour Energy, an FDA spokeswoman said Thursday.

“FDA is continuing to investigate reports of illness, injury or death of people who took products marketed under the label 5-Hour Energy,” Shelly Burgess told AFP in an email.

There have been a total of 92 patient reports, including 33 hospitalizations and 13 deaths, she said.

She emphasized, however, that “the existence of an adverse event report does not necessarily mean that the product identified in the report actually caused the adverse event.”

The FDA warns that energy drinks — rich in stimulants like caffeine — cannot substitute for rest or sleep and advises people to consult a doctor before consuming them, to ensure the product will not aggravate any undiagnosed medical problem.

This is the second investigation the FDA has launched in the last two months into potentially harmful effects from energy drinks.

In late October, the agency announced it was investigating five deaths and a non-fatal heart attack for possible links to consumption of Monster Energy drinks.

Monster Beverage is also being sued in California by the family of Anais Fournier, a teenager who died of an arrhythmia in December 2011, allegedly after drinking two cans of Monster Energy over a 24 hour period.

Her parents accused the company of not warning consumers of the potential dangers of its product.

Two Democratic senators, Dick Durbin from Illinois and Richard Blumenthal from Connecticut, have demanded a meeting with FDA director Margaret Hamburg “to discuss the steps the agency is taking to ensure the safety of these products,” according to a release.

Living Essentials, the maker of 5-hour Energy, said it was taking the reports of deaths very seriously, while insisting it has not yet been proven any deaths were actually caused by consuming 5-Hour Energy.